Communications:Satellite Ground Station Logs - Key Observations/Analysis
This Reference Item is an extract from the Safety Investigation Report MH370/01/2018 which provides an analysis of the Satellite Ground Station Logs. The additional information supports the chronology of events related to Malaysia Airlines flight MH370.
Each event in this chronology has been linked to a Timeline Event in the main Timeline articles on this site. This provides a cross-link or check on the well known events. (The Timeline includes other events not included in this chronology).
2.5.1 Summary of Key Observations of the SATCOM Ground Station Logs
The key observations of the SATCOM Ground Station Logs, with an assessment, are summarised below:
1) Prior to take-off, the SATCOM Logged On (normally) a number of times, the last time being at 1600, when it sent a valid Flight ID to the Ground Earth Station (GES). The SATCOM link was available for both voice and data (known as Log-On Class 3).
2) After take-off, the In-Flight Entertainment System (IFE) Short Messaging System (SMS) e-mail application sent a normal beginning of flight message at 1642 (containing the correct Airborne Earth Station (AES ID), Flight ID “MAS370”, origin airport “WMKK”, and destination airport “ZBAA”), indicating that the IFE was receiving the valid Flight ID, origin airport and destination airport from Airplane Integrated Management System (AIMS) and the ICAO (AES) ID from the Satellite Data Unit (SDU) at this time.
3) The SATCOM link was available for most of the flight, excluding periods leading up to 1825 on 07 March 2014 and 0019 on 08 March 2014.
4) When the SATCOM link was re-established at the above times, no Flight ID was present. This implies that a valid Flight ID probably stopped being sent to SATCOM at some time between 1642 (when the IFE reported the correct Flight ID) and 1825 (when the SATCOM Logged On with no Flight ID) on 07 March 2014. The possible reasons for the link losses and the subsequent Log-Ons that took place at 1825 and 0019 have been investigated and are detailed in tables in Section 2.5.2. There are many quite complicated scenarios that could have caused the 1825 Log-On. However, the most likely reason is a lengthy power interrupt to the SATCOM. The most likely reason for the 0019 Log-On was also a power interrupt to the SATCOM.
5) During the two in-flight Log-Ons at 1825 and 0019, the GES recorded abnormal frequency offsets for four burst transmissions from the SATCOM. After extensive analysis, the following explanations have emerged. The 1825 Log-On Request had a non-zero BER and could therefore have been logged at the Ground station with a BFO measurement error suggesting that the BFO figure may not be reliable.
a) 1825 Log-On Acknowledge - Most likely due to the power-on drift of the SDU Oven Controlled Crystal Oscillator (OCXO), thus endorsing the belief that the 1825 Log-On was preceded by a lengthy power interrupt.
b) 0019 Log-On Request - Could have been due to uncompensated vertical velocity, indicating that the aircraft was likely to be descending at this time. Alternatively, it could have been due to the OCXO warm up drift, or it could have been due to a combination of uncompensated vertical velocity and OCXO warm up drift.
c) 0019 Log-On Acknowledge - Could have been due to uncompensated vertical velocity, indicating that the aircraft was likely to be descending at this time. Alternatively, it could have been due to the OCXO warm up drift, or it could have been due to a combination of uncompensated vertical velocity and OCXO warm up drift.
d) It has not been possible to attribute specific correction values to the 1825 Log-On Acknowledge and 0019 Log-on Request and Log-On Acknowledge BFOs, so it was excluded from the Doppler calculations undertaken by the Aircraft Flight Path/Performance Subgroup. In the case of the 1825 Log-On Acknowledge, the following subsequent bursts were used instead, as the frequency is more stable at these times:
i) 1828:05.904 Data-3 R-Channel burst.
ii) 1828:14.905 Data-3 R-Channel burst.
6) There is no indication of the SATCOM link being manually Logged Off from the cockpit (via a Multi-function Control Display Unit [MCDU]). Such activity would have been captured in the GES logs, but it was not.
7) No Data-2 Aircraft Communications Addressing and Reporting System (ACARS) traffic was observed after 1707 on 07 March 2014.
8) The IFE equipment set up two ground connections over SATCOM (for the SMS e-mail application and Built-In Test Equipment (BITE) application) after the SATCOM re-established the link at 1825 on 07 March 2014 (normal), but not after the SATCOM re-established the link at 0019 on 08 March 2014 (abnormal). In the 0019 case, it is possible that the IFE was no longer powered, or failed, or that the IFE and/or the SATCOM became inoperative before the connections could be set up. At no time during the flight was any user data sent over the link by means of the SMS/e-mail application.
9) Two Ground-to-Air Telephony Calls were placed to the cockpit from the MAS Airline Operations Centre at Airline Operational Communications (AOC) Q10 priority level at 1839 and at 2313 on 07 March 2014. Neither of the calls was answered.
10) The SATCOM responded normally to a series of roughly hourly Log-On Interrogations from the Perth GES, up to and including a Log-On Interrogation at 0011 on 08 March 2014. The two unanswered ground to air calls at 1839 and 2313 reset the Perth GES inactivity timer and hence the Log-On Interrogations were not always hourly.
11) The SATCOM transmissions during the two in-flight Log-Ons and five Log-On Interrogations form the seven ‘handshakes’ that have been used by the Flight Path/Performance Subgroup to calculate the seven geographical ‘arcs’.
12) The last transmission received from the SATCOM occurred at 0019 on 08 March 2014 and the SATCOM failed to respond to a series of three Log-On interrogations starting at 0115 on 08 March 2014. This implies that the SATCOM probably became inoperative at sometime between 0019 and 0115 on 08 March 2014.
Source: Malaysian ICAO Annex 13 Safety Investigation Team for MH370, 02 July 2018, Safety Investigation Report MH370/01/2018
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